1. Field of the Invention
The present invention relates to a biodegradation accelerator of hydrophobic pollutants such as hydrocarbons, of oil/water microemulsions, also called nutrient microemulsions, which are consumable by microorganisms.
2. Description of the Related Art
The formulation of the nutrient microemulsions in the past has represented a significant advance in the marketing of additives which are useful as biodegradation accelerators. For example, French Patent Nos. 2,490,672 and 2,512,057 describe such accelerators, which are formulated as an internal phase of an aqueous solution of nitrogenous and phosphorus compounds, preferably phosphorous surfactants, this phase being dispersed in an external hydrophobic phase formed of an easily assimilated carbon source. In these emulsions, the nitrogenous compounds employed are, for example, amino acids, proteins, or urea, and phosphorous compounds of surfactants of the alkyl or alkenyl phosphoric ester type. The hydrophobic external phase is formed of a carbon source easily assimilated by microorganisms, such as vegetable oils or, animal oils and fatty acids, which are selected in order to be compatible with the products to be degraded.
The effectiveness of these known emulsions as biodegradation accelerators has been clearly demonstrated in numerous industrial applications, especially in the treatment of effects of marine pollution resulting from accidental spills of hydrocarbons and in the treatment procedures which are directed to the rehabilitation of soil contaminated with hydrophobic pollutants such as described in patent WO 95/06715.
Despite the qualities of nutrient microemulsions, their use remains limited on account of difficulty in use, in particular at temperatures below 10.degree. C.
The microemulsions described in the state of the art are generally applied in spray form to the contaminated zones or mixed with polluted soil. They must therefore exhibit certain fluidity and a certain stability favoring such applications. Yet, these microemulsions have the disadvantage of separating into two immiscible phases near 0.degree. C. In addition, whenever an ambient temperature lower than 20.degree. C. is reached, these microemulsions become very viscous (more than 1,000 mPa.multidot.sec), which makes their use on the soil very tricky or even impossible in certain forms of application such as by a spray.
Of course, attempts have been made to remedy this major drawback by the addition of organic compounds, such as alcohols and glycol ethers, to decrease the viscosity of these microemulsions at these temperatures, as is mentioned in application WO 9/07508. Thus, by adding from 10 to 15% ethylene glycol butyl ether, a decrease in the viscosity to approximately 200 mPa.multidot.sec at 20.degree. C. has been observed, allowing spraying of the product with conventional equipment at this temperature, or an easier spreading. However, to apply these microemulsions at a lower temperature, in particular below 10.degree. C., it is currently advisable either to store the microemulsions at 20.degree. C. in order to spray the microemulsions at this temperature, or to reheat the microemulsions on site while the microemulsions are reformed and/or become fluid again. It is a major drawback for the user who, as the product is transformed, is no longer certain of the quality of his product. Therefore, it is understood why the use of this biodegradation accelerator, otherwise remarkable in its effectiveness, has not been widely extended to all applications for marine or terrestrial biodegradation, in particular, in cold countries.